Download CS434/534: Topics in Networked (Networking) Systems

CS434/534: Topics in Networked
(Networking) Systems
Mobile System: Android (Single App/Process)
Yang (Richard) Yang
Computer Science Department
Yale University
208A Watson
Email: yry@cs.yale.edu
http://zoo.cs.yale.edu/classes/cs434/
Admin.
❒ Project planning
❍ Start: Apr. 5
• A meeting w/ instructor; Due: team, potential topics
❍
Checkpoint I: Apr. 13 (updated; Thursday)
• Initial ideas; survey of related work; feedback from
instructor/TF
❍
Checkpoint II: Apr. 20 (updated)
• Initial design; feedback from instructor/TF
❍
Checkpoint III: Apr. 27 (updated)
• Design refined; key components details
❍
Final report: May 4
• No more than 6 page write up
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Recap: TinyOS (Sensors)
❒ Simple clean software
framework
❍
❍
❍
component
interface
configurations
❒ Aggregation
(framework)
❍
an app (configuration)
at a time, linking
only necessary
components
❒ Execution model
❍ one for event
❍ one for task
interface ADC {
async command result_t getdata();
async command result_t
getContinuousData();
event result_t dataReady(uint 16_t data);
}
configuration SenseTask {
// this module does not provide any interfaces
}
implementation
{
components Main, SenseTaskM, LedsC,
TimerC, DemoSensorC as Sensor;
Main.StdControl -> TimerC;
Main.StdControl -> Sensor;
Main.StdControl -> SenseTaskM;
SenseTaskM.Timer ->
TimerC.Timer[unique("Timer")];
SenseTaskM.ADC -> Sensor;
SenseTaskM.Leds -> LedsC;
}
3
Recap: Mobile UI Framework
❒ Limited screen real estate
❍ one thing at a time
❒ Limited resources: more dynamic system
management on app life cycle
❍
give app chances to adapt, better mem management
4
Recap: Java ME
❒ To accommodate heterogeneous mobile
devices, define configurations and profiles
❒ The Mobile Information Device Profile
(MIDP) provides a simple, representative
programming framework
Lifecycle
callbacks
- startApp
- pauseApp
- destroyApp
d=Display.getDisplay(this)
d.setCurrent(disp)
MIDP
Current
Displayable
A set of
command
Command
listener
5
HelloWorldMIDlet.java
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class HelloWorldMIDlet extends MIDlet
implements CommandListener {
private Command exitCommand;
private Display display;
private TextBox t;
public HelloWorldMIDlet() {
display = Display.getDisplay(this);
exitCommand = new Command("Exit", Command.EXIT, 2);
t = new TextBox(“CS434", "Hello World!", 256, 0);
t.addCommand(exitCommand);
t.setCommandListener(this);
}
public void startApp() { display.setCurrent(t); }
public void pauseApp() { }
public void destroyApp(boolean unconditional) { }
public void commandAction(Command c, Displayable s) {
if (c == exitCommand) {
destroyApp(false);
notifyDestroyed();
}
}
}
6
Recap: General Mobile GUI App Structure
App lifecycle
callbacks/custom
-start
-pause
-…
App
Display
Composite
Display
Display
Composite
Display
Display
Display
Composite
Display
Display
Composite
Display
Display
Composite
Display
Display
Display
Mobile GUI App Workflow: Handle Events
App lifecycle
callbacks/custom
-start
-pause
-…
App
Display
Composite
Display
Display
Composite
Display
Composite
Display
Display
Event
Handler
Event
Handler
Display
Data/
Model
Display
Data/
Model
Recap
❒ Key design points (so far) for
mobile GUI app framework
How to specify app life cycle customization
❍ How to specify display
❍ How to specify event scheduling
❍
• How to link event, display, handler, data
9
Outline
❒ Admin and recap
❒ Mobile/wireless development framework
❍ GNURadio
❍ Sora
❍ TinyOS
❍ Java ME
❍ Android
10
Android
❒ A mobile OS based on Linux
❍
❍
❍
Customized Linux kernel 2.6 and
3.x (Android 4.0 onwards), e.g.,
• default no X Windows, not full set of
GNU libs
Apply OS concepts for mobile
contexts, e.g.,
• each app is considered one Linux user
• by default, every app runs in its own
Linux process
• each process has its own virtual
machine (VM), so an app's code runs
in isolation from other apps.
New key components, e.g.,
• binder for IPC
• power management wakelock
11
Android Architecture
12
Android Tools
❒ Android SDK Manager (android)
❒ Android emulator
❒ Android debug bridge (adb) can connect to an
Android device and start a shell on the
device
❒ See http://developer.android.com/tools/workflow/index.html
Outline
❒ Admin and recap
❒ Mobile/wireless development framework
❍ GNURadio
❍ Sora
❍ TinyOS
❍ Java ME
❍ Android
• Platform overview
• Basic app/view/event handling
14
Allows external XML
resource files to
specify views
Mapping to Android
App lifecycle
callbacks/custom
-start
-pause
-…
App
Display
Composite
Display
-How to specify the
customized callbacks:
extend Activity class
Display
Composite
Display
Composite
Display
-How to link the callbacks defined
in view to listener/controller:
View.set…Listener()
Display
Event
Handler
Event
Handler
Display
Data/
Model
Display
Data/
Model
Application Framework (Android):
Key Concepts
❒ Activity
❒ View/ViewGroup (Layout)
❒ External resources
16
Activity
❒ A single, focused thing that the user can do
❒ A typical app consists of multiple activities
(why?)
❒ Typically organized as a Stack
❍ Top Activity is visible
❍ Other activities are stopped
❍ Back button to traverse the
Activity Stack
Simple Activity Example
❒ Create Hello434
18
Activity: Manifest File
❒ To facility launching and managing Activities,
each activity is announced in a manifest file
Instead of a hardcode
string in code, defines
in res/strings
Manifest the activity
Android Project Resources
20
Activity: Example
// MainActivity.java
public class MainActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
// savedInstanceState holds any data that may have been saved
// for the activity before it got killed by the system (e.g.
// to save memory) the last time
super.onCreate(savedInstanceState);
setContentView(… ); // set a View
}
https://developer.android.com/guide/components/activities/intro-activities.html
Android Activity
Life Cycle
22
Simple Activity Example
❒ Create Hello434
❒ Show life cycle
23
View
❒ A view component is a building block for user
interface components.
❒ Two types of views
❍
❍
Leaf: TextView, EditText, Button, Form,
TimePicker… ListView
Composite (ViewGroup): LinearLayout,
Relativelayout, …
http://developer.android.com/guide/tutorials/views/index.htm
View
https://developer.android.com/guide/topics/ui/overview.html
Programmatic Definition of View
// MainActivity.java
public class MainActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
// savedInstanceState holds any data that may have been saved
// for the activity before it got killed by the system (e.g.
// to save memory) the last time
super.onCreate(savedInstanceState);
TextView tv new TextView(this);
tv.setText("Hello!“);
setContentView(tv);
}
Simple Activity Example
❒ Create Hello434
❒ Show life cycle
❒ Use programmatic definition of view
27
Define View by XML
Access View Defined by XML
main.xml
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
}
…
TextView myTextView =
(TextView)findViewById(R.id.myTextView);
<?xml version=”1.0” encoding=”utf-8”?>
<LinearLayout
xmlns:android=”http://schemas.android.co
m/apk/res/android”
android:orientation=”vertical”
android:layout_width=”fill_parent”
android:layout_height=”fill_parent”>
<TextView
android:id=”@+id/myTextView”
android:layout_width=”fill_parent”
android:layout_height=”wrap_content”
android:text=”Hello World, HelloWorld”
/>
</LinearLayout>
External Resources
❒ Compiled to numbers and included in R.java file
30
Linking Views and Handlers/Controllers
❒ onKeyDown. onKeyUp
❒ onTrackBallEvent
❒ onTouchEvent
registerButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {….}}
myEditText.setOnKeyListener(new OnKeyListener() {
public boolean onKey(View v, int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_DOWN)
if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) {
…
return true;
}
return false;
}});
}
Example: TipCalc
Set listener:
public class TipCalcActivity extends Activity {
…
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_tip_calc);
}
}
…
Button calc = (Button)findViewById(R.id.calculate);
calc.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View view) {
…
}
);
32
Example: TipCalc
Handler:
@Override
public void onClick(View arg0) {
EditText amountText =
(EditText)findViewById(R.id.amount_value);
// get input
double amt=Double.parseDouble(amountText.getText().toString());
// compute output
double tipD = amt * 0.15;
// set UI
String tipT = String.format("%.2f", tipD);
TextView tipText = (TextView)findViewById(R.id.tip_value);
}
tipText.setText(tipT);
33
Simple Activity Example
❒ Create Hello434
❒ Show life cycle
❒ Use programmatic definition of view
❒ Add event handling
34
Summary: Most Basic Android UI App
Software Concepts
❒ Activity
❒ UI (View/ViewGroup)
❍ External definition of views in XML
❍ findViewById() to reduce coupling
❒ Link view events to event handlers
❍ set…Listener()
❒ Other concepts such fragments which we
skip
35
Outline
❒ Admin and recap
❒ Mobile/wireless development framework
❍ GNURadio
❍ Sora
❍ TinyOS
❍ Java ME
❍ Android
• Platform overview
• Basic concepts
– Activity, View, External Resources, Listener
• Execution model and inter-thread communications
– Handler, ASyncTask
36
Android Execution Model
❒ When an application component starts and
the application does not have any other
components running, the Android system
starts a new Linux process for the
application with a single thread of execution
❒ The very important thread is also called the
"main" thread
in charge of dispatching events to the appropriate
user interface widgets, including drawing events.
❍ interacts with components from the Android UI
toolkit
❍
https://developer.android.com/guide/components/processes-and-threads.html
37
Event Handler Execution
❒ Event handler
UI
events
system
events
executed by
the main/UI
thread
message
message
Looper
UI
(main)
thread
message
http://www.java2s.com/Open-Source/Android/androidcore/platform-frameworks-base/android/os/Looper.java.htm
38
Event Handler and Responsiveness
❒ Event handler
UI
events
blocks events in
the msg queue
from being
processed
=>
slow running
handler leads to no
UI response
system
events
message
message
Looper
UI
(main)
thread
message
http://developer.android.com/guide/practices/responsiveness.html
39
Responsiveness: Numbers (Nexus One)
❒ ~5-25 ms – uncached flash reading a byte
❒ ~5-200+(!) ms – uncached flash
writing tiny
amount
❒ 100-200 ms – human perception of slow
action
❒ 108/350/500/800 ms – ping over 3G. varies!
❒ ~1-6+ seconds – TCP setup + HTTP fetch of
6k over 3G
40
Event Handler and ANR
❒ Android system
detects no
response
❍
Main thread
(“event”/UI) does
not respond to
input in 5 sec
41
Discussion
❒ What are some events that may take a while
to be processed?
Time consuming loading process, e.g., slow
onCreate
❍ Heavy computation, e.g., voice recognition, update
map display
❍ Networking access
❍…
❍
❒ What are some design options if an event
may take a while to be processed?
42
Typical Design Guidelines
❒ Notify user
❍ E.g., progress bar, progress dialog
❍ A splash screen
❒ If possible, non-blocking, incremental update UI
❍ E.g., gradual add items to map
❒ Whenever possible, release UI thread ASAP
❍ Keep event handler simple
❍ Post heavy processing off the UI thread
43
Example: Background Thread
❒ Use a background thread to do the task
❒ Background thread behavior controlled by
state
❒ State controlled by event handler
44
Example: LoadingScreen
public class LoadingScreen extends Activity implements Runnable {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.loading);
}
// start a new thread to load
Thread thread = new Thread(this);
thread.start();
public void run(){
longRunningTask();
setContentView(R.layout.main);
}
}
…
Conflict
with UI
thread
45
Background Thread vs UI Thread
❒ Problem:
❍ Background thread and UI thread are running
concurrently and may have race conditions if they
modify UI simultaneously (e.g., UI switches to a
different orientation)
❍ A major sin of programming: concurrency bugs
46
Solution
❒ Background thread does not directly modify
UI: send msg to UI thread, who processes
the msg
❒ Android Methods
❍ Activity.runOnUiThread(Runnable)
❍ View.post(Runnable)
❍ View.postDelayed(Runnable, long)
47
Example
public void onClick(View v) {
new Thread(new Runnable() {
public void run() {
// a potentially time consuming task
final Bitmap bitmap =
processBitMap("image.png");
mImageView.post(new Runnable() {
public void run() {
mImageView.setImageBitmap(bitmap);
}
}); // post
} // run
}).start();
}
48
Android Handler
❒ Android’s mechanism to send and
process Message and Runnable objects
associated with a thread's MessageQueue.
❒ Each Handler instance is associated with a
single thread and that thread's message
queue
❍
❍
❍
A handler is bound to the thread / message queue of
the thread that creates it
from that point on, it will deliver messages and
runnables to that message queue
That thread processes msgs
49
Android Handler
50
Using Handler: Examples
❒ There are two main uses for a Handler
❍
to schedule messages and runnables to be
executed as some point in the future
• postDelayed(Runnable, delayMillis)
❍
to enqueue an action to be performed on a
different thread than your own.
• post(Runnable)
51
Handler
public class MyActivity extends Activity {
[...]
// Need handler for callbacks to the UI thread
final Handler mHandler = new Handler();
// Create runnable task to give to UI thread
final Runnable mUpdateResultsTask = new Runnable() {
public void run() {
updateResultsInUi();
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
[...]
}
52
Handler
protected void startLongRunningOperation() {
// Fire off a thread to do some work that we shouldn't do directly in the UI thread
Thread t = new Thread() {
public void run() {
mResults = doSomethingExpensive();
mHandler.post(mUpdateResultsTask);
}
};
t.start();
}
private void updateResultsInUi() {
// Back in the UI thread -- update our UI elements based on the data in mResults
[...]
}
}
53
Example: Fixing LoadingScreen
public class LoadingScreen extends Activity implements Runnable {
private Handler mHandler = new Handler(); // UI handler
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.loading);
// start a new thread to load
Thread thread = new Thread(this);
thread.start();
}
Conflict
Conflict with
with UI
UI thread
thread
}
public void run(){
longTask();
mHandler.post(mSetFinalViewTask);
}
private Runnable mSetFinalViewTask = new Runnable() {
public void run() {
setContentView(R.layout.main);
}
};
54
Common Pattern
private Handler mHandler = new Handler(); // UI handler
private Runnable longTask = new Runnable() {
// processing thread
public void run() {
while (notFinished) {
// doSomething
}
mHandler.post(taskToUpdateProgress);
// mHandler.post(taskToUpdateFinalResult)
};
Thread thread = new Thread(longTask);
thread.start();
55
AsyncTask as Abstraction
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
protected Long doInBackground(URL... urls) { // on some background thread
int count = urls.length; long totalSize = 0;
for (int i = 0; i < count; i++) {
totalSize += Downloader.downloadFile(urls[i]);
publishProgress((int) ((i / (float) count) * 100));
}
return totalSize;
}
protected void onProgressUpdate(Integer... progress) { // on UI thread!
setProgressPercent(progress[0]);
}
protected void onPostExecute(Long result) { // on UI thread!
showDialog("Downloaded " + result + " bytes");
}
}
new DownloadFilesTask().execute(url1, url2, url3); // call from UI thread!
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